Twenty-first century science establishes itself primarily on the basis of facts, proofs and clever hypothesises. Many students and scientists now take this method for granted. Scientific theories, however, were not always this easy to establish, since anything against biblical accounts and the norms of society was considered heresy. The eighteenth and nineteenth century scientists wrote very cleverly to persuade their readers to accept their arguments. To validate their points of view, they employed several writing and rhetoric strategies. Some of the most effective writing and rhetoric strategies employed by scientists such as Joseph Priestly, Isaac Newton, Georges Cuvier and Charles Darwin are appeal to authority, appeal to emotion, and the use of structure.